The Wadden Sea (Dutch: Waddenzee; German: Wattenmeer; Low German: Wattensee or Waddenzee; Danish: Vadehavet; West Frisian: Waadsee; North Frisian: di Heef) is an area between land and sea that is covered by water during high tide. It is located in the southeastern part of the North Sea, between the coast of northwestern Europe and the low-lying Frisian Islands. This area includes shallow water, tidal flats, and wetlands. It is home to many different types of plants and animals and is an important place for birds to live and travel. In 2009, the parts of the Wadden Sea in the Netherlands and Germany were added to UNESCO’s World Heritage List. The Danish part was added in June 2014.
The Wadden Sea extends from Den Helder, in the northwest of the Netherlands, past the large river mouths in Germany, to Skallingen in Denmark. It covers about 500 kilometers (310 miles) of coastline and has an area of roughly 10,000 square kilometers (3,900 square miles). In the Netherlands, it is separated from the IJsselmeer by the Afsluitdijk. In the past, this region often experienced large floods that caused many deaths. Examples include the Saint Marcellus’ floods in 1219 and 1362, the Burchardi flood in 1634, and the Christmas Flood in 1717. Some of these floods changed the coastline. To protect the area, many dikes and causeways were built. Because of these structures, recent floods have caused few or no deaths, even though some dikes have occasionally been overtopped in recent years. This makes the Wadden Sea one of the most heavily modified natural areas on Earth.
Environment
The word "wad" comes from the Frisian and Dutch languages and means "mud flat." In Low German and German, it is called "Watt," and in Danish, it is "Vade." This area is known for large tidal mud flats, deeper tidal channels (called tidal creeks), and the islands found within these regions. This land is constantly shaped by the movement of the sea and the land.
The landscape was largely formed by storm tides between the 10th and 14th centuries. These powerful tides flooded and removed old peat land that was behind coastal dunes. The islands that exist today are leftover parts of these former dunes.
To the north, near the North Sea, the islands have dunes and wide sandy beaches. Toward the Wadden Sea, the coastline is lower and shaped by tides. Waves and ocean currents slowly change both land areas and coastlines. For example, the islands of Vlieland and Ameland have shifted eastward over time. They have lost land on one side and gained land on the other.
Rising sea levels are a major threat to low-lying coastal areas with gentle slopes, such as the tidal flats of the Wadden Sea. However, recent studies show that the current rate of sea level rise (3.7 mm per year) is slower than the rate at which sediment builds up on most tidal flats, especially along the German coast. Tidal flats in the Dutch Wadden Sea are also gaining sediment, but at a slower pace.
Fauna
The Wadden Sea is known for having many plants and animals, especially birds. Many waders, ducks, and geese use the area as a place to rest during their travels or to spend the winter. The area also supports gulls, terns, herons, Eurasian spoonbills, and birds of prey, including a small group of white-tailed eagles that are growing in number. However, the variety of life in the Wadden Sea is less than it was before. In the past, greater flamingos and Dalmatian pelicans were common, especially during a time when the climate was warmer. Because of human actions and changes in the environment, some species have disappeared, while others may move away.
Larger fish, such as rays, Atlantic salmon, and brown trout, still live in parts of the Wadden Sea. However, European sea sturgeon only remain in the area because of a project to bring them back. The last natural group of houting, a type of fish, lives in the Danish part of the Wadden Sea. This group has been used to help reintroduce houting to areas farther south, but scientists are still unsure if this fish is the same as the one that once lived in the southern Wadden Sea. European oysters once formed large groups in the region but disappeared a few decades ago because of disease and the spread of the invasive Pacific oyster, which now lives in the Wadden Sea. The southwestern part of the Wadden Sea has lost much of its biodiversity. The Rhine River, which once carried the most water into this area, has been greatly reduced because of dams. As a result, about 90% of the species that once lived in this part of the Wadden Sea are now at risk.
The Wadden Sea is an important home for both harbor and gray seals. Harbour porpoises and white-beaked dolphins are the only whales that live in the sea year-round. These animals were once gone from the southern part of the sea but have returned. Many other whales visit the area only during certain times of the year or rarely. In the past, North Atlantic right whales and gray whales (now extinct in the North Atlantic) lived in the region, possibly using the shallow, calm waters for feeding and raising young. It is believed that these whales were hunted to extinction by people living along the shore during medieval times. While these whales are generally considered gone from the area, a possible right whale was seen near beaches in the Netherlands in 2005. Recent increases in North Atlantic humpback whales and minke whales may lead to more visits or even a return to areas like Marsdiep. Scientists also think that local populations of bottlenose dolphins, which once disappeared, may recover in the future.
Conservation
Invasive species, such as algae, plants, and small animals introduced by people, are harming native species in the area.
Each of the three countries has chosen Ramsar sites in the region (see Wadden Sea National Parks).
Although the Wadden Sea is not yet listed as a shared Ramsar site, a large part of the Wadden Sea is protected through joint efforts by all three countries. The governments of the Netherlands, Denmark, and Germany have been working together since 1978 to protect and preserve the Wadden Sea. Cooperation includes managing, monitoring, researching, and handling political issues. In 1982, the three countries signed a Joint Declaration to help coordinate protection efforts. In 1997, they created a Trilateral Wadden Sea Plan.
In 1986, the Wadden Sea Area was named a biosphere reserve by UNESCO.
In June 2009, the Wadden Sea (including the Dutch Wadden Sea Conservation Area and the German Wadden Sea National Parks of Lower Saxony and Schleswig-Holstein) was added to the World Heritage list by UNESCO. A small change to the boundaries in 2011 added the Hamburg Wadden Sea National Park to the site, and the Danish part was added in 2014. The state of Bremen, which covers part of the Weser River estuary, is not involved. Conservation efforts are managed by the Common Wadden Sea Secretariat, located in Wilhelmshaven.
Recreation
Many of the islands have been popular places for vacation since the 1800s. Walking on the wet sandy areas during low tide has become a popular activity in the Wadden Sea. People also enjoy boating for fun in this area.
Literature
The German section of the Wadden Sea was the location for the 1903 novel The Riddle of the Sands by Erskine Childers and the 1915 novel Nesthäkchen in the Children's Sanitorium by Else Ury.
Wadden Sea Region
The area near the Wadden Sea, which includes the Frisian islands and the marshes along the mainland coast, is also known as the Wadden Coast. In Germany, this region is called the North Sea Coast (Nordseeküste). The flooded areas protected by dikes and the salt marshes in the Wadden Sea region, such as the Elbe Marshes, are referred to in Germany as North Sea coastal marshes (Nordseemarschen).
More recently, terms like Waddenland, Wadden Sea area, and Wadden Sea Region have been used. The term "Wadden Sea Region" is generally understood to include all coastal areas around the Wadden Sea that are part of a joint effort between Denmark, Germany, and the Netherlands. This entire area is known for its long history of cultural heritage, which dates back to the Roman Iron Age and the Middle Ages. It largely matches the area internationally known as Frisia. Between 2002 and 2023, groups and organizations from the Wadden Sea Region worked together in a group called the Wadden Sea Forum (WSF).